The present invention relates to a microwave oven, and more particularly, to an apparatus and a method for heating a container containing food or the like in a microwave oven by judging a quantity of food in the container on the basis of a change of an initial temperature of the food and compensating for variations between a detected temperature and a cooking temperature.
In a general method for heating a container in the microwave oven, the container is heated in a heating mode until the temperature detected by an infrared sensor is raised to the prescribed temperature.
FIG. 1 is a block diagram showing the structure of the conventional microwave oven.
In the conventional microwave oven, as shown in FIG. 1, the cooking chamber 1 has an opening 4 formed at the upper portion of its side wall. An infrared sensor 5 for sensing the temperature of the container 7 is set therein through the opening 4. Further, the microwave oven includes a heating unit 3 generating microwaves on the basis of the temperature detected by the infrared sensor 5 and a judging unit 6 controlling the operation of the object.
In the lower portion of the cooking chamber 1, a motor 8 is provided to drive a turntable 2 according to a control signal for the judging unit 6. The turntable 2 is rotatably mounted within the cooking chamber 1 on the upper portion of the shaft of the motor 8. On the turntable 2, the container 7 containing the food to be cooked is located.
The judging unit 6 controls operation of the heating unit 3 and the motor 8 after a heat starting key is actuated. The judging unit 6 includes the structure indicated in FIG. 2. This structure is described in detail as follows. The judging unit 6 comprises a key input unit 6a for setting a cooking temperature corresponding to the selected food or for inputting a starting signal; a set temperature storing unit 6b for storing the set cooking temperature; a current temperature storing unit 6c for temporarily storing the current temperature detected by the infrared sensor 5; a display unit 6d including a liquid crystal display to indicate the set and current temperature; and an output controlling unit 6e for comparing the set temperature with the current temperature to thereby control the output.
With the signal detected by the sensor 5, the current temperature is judged by the judging unit 6. When the detected current temperature is lower than the set temperature, the judging unit 6 operates the heating unit 3 until the current temperature reaches the set temperature for completion of cooking.
The cup 7 within the cooking chamber 1 is heated by the microwaves generated by the heating unit 3. When starting the heating operation, the turntable 2 is rotated to evenly apply the microwaves to the container 7.
Hereinafter, the operation of the conventional microwave oven is described in detail accompanying the drawings.
FIG. 3 is a flow chart illustrating a cooking operation of a conventional microwave oven.
The container 7 is first put on the turntable 2 in the cooking chamber 1, the key input unit 6a is operated to set the appropriate cooking temperature, and the cooking start key is actuated. The set cooking temperature is memorized in the set temperature storing unit 6b. When the cooking starting key is activated, the heating unit 3 is driven according to a controlling signal from the output controlling unit 6e. As a result, microwaves are generated by the heating unit 3 so that the container 7 with food therein is heated. Because of the heating operation of the heating unit 3, the temperature of the container 7 gradually increases.
On the other hand, the temperature of the container 7 is detected by the infrared sensor 5 through the opening 4.
The output controlling unit 6e reads the temperature stored in the current temperature storing unit 6c and the cooking temperature stored in the set temperature storing unit and compares them (step 110). When the detected current temperature is lower than the cooking temperature, the heating unit 3 is continuously driven by the output controlling unit 6e to heat the container 7. When the current temperature is raised to at least the set cooking temperature, the output controlling unit 6e stops operation of the heating unit 3 for completion of cooking (step 120).
The container 7 located in the cooking chamber 1 may include a cup containing a food such as water or milk. Since the container is heated by the microwaves generated by the heating unit 3, the practical temperature of the food 9 in the container 7 can be higher than the cooking temperature when the current temperature is detected by the infrared sensor 5. Particularly, when a small amount of food 9 is in the container, the difference between the actual temperature of the food 9 and the set cooking temperature is larger.
This difference is caused by heat conduction. That is, the heat of the food 9 is transmitted to the container 7 so that the food 9 is at a higher temperature than that of the container. Further, the temperature deviation between the various parts of the container 7 and the food causes a temperature difference between the container 7 and the food according to quantity of the food present.
For example, when the container is heated to a set cooking temperature of 50.degree. C.,
if the amount of food in the container is 100 ml, its temperature is 73.degree. C.; PA1 if the amount of food in the container is 150 ml, its temperature is 69.degree. C.; PA1 if the amount of food in the container is 200 ml, its temperature is 63.degree. C.; PA1 if the amount of food in the container is 250 ml, its temperature is 51.degree. C.; PA1 if the amount of food in the container is 300 ml, its temperature is 51.degree. C.; and PA1 if the amount of food in the container is 350 ml, its temperature is 43.degree. C.
In the conventional method of heating a container in the microwave oven using the infrared sensor 5, a small quantity of food is blocked from the sensing region of the infrared sensor 5 by the sides of the container since the infrared sensor 5 is mounted at the upper portion of the side wall (as shown in FIG. 4).
In the conventional microwave oven, therefore, the actual food temperature is in the container has the great difference temperature from the set cooking temperature. As a result, there is some inconvenience for the user.